Field of the Invention
The invention relates to a method for testing an electronic component for defects, in which both an automatic optical inspection (AOI) and non-destructive material testing (NDT) by means of X-radiation are carried out.
By “electronic components” in the context of this invention is meant, among other things, printed circuit board assemblies, wafers—silicon slices with etched structures such as for example micro solder balls—and electronic components, such as for example semiconductors and LEDs.
Description of Related Art
In principle, the testing of a printed circuit board assembly—hereafter printed circuit board assemblies will be referred to simply as circuit boards—and of a wafer or of a receiving tray for components is the same. The difference between the testing of a circuit board and a wafer or an electronic component, for example a semiconductor, is essentially that the wafer or the component is clearly positioned in a firmly predefined holder—a kind of receiving tray. This holder can for example be in the form of a rectangular tray, analogous to the rectangular geometry of a circuit board. Several wafers or electronic components can be positioned on one receiving tray.
For simplification, statements are only made for circuit boards below; however, these always also apply equally to wafers or electronic components arranged in a receiving tray, unless explicitly indicated otherwise at individual points.
When testing circuit boards for defects, it is known to examine the circuit boards within the production line by means of an AOI. Errors in the alignment of the components affixed to the circuit board or defects of the solder connections between the circuit board and the components connected thereto are detected here. The possible defects include for example solder bridges, missing solder connections, and solder connections with porosities. However, during optical examination by means of AOI, it is only possible to find defects that are visible from the outside; hidden defects cannot be detected therewith. In order to be able to recognize these defects, the circuit board is subjected to an NDT method using X-radiation, in addition to the AOI. The non-visible points are examined by means of radioscopy without damaging the circuit board. From a combination of the results of the AOI and the X-ray NDT, it can then be decided whether the circuit board can continue in the production line, or whether it is a reject or has to be subjected to reworking.
This combined testing with AOI and X-ray NDT can either be carried out in that the X-ray NDT test device is integrated in the production line, or is arranged separate therefrom. In the first alternative with integrated X-ray NDT test device, it is problematic that the entire production line is at a standstill when maintenance or repair operations have to be carried out on the X-ray NDT test device; moreover each production line needs its own X-ray NDT test device, giving rise to very high costs for the entire production line.
In the second alternative with separately arranged X-ray NDT test device, the costs per production line are lower, as a single X-ray NDT test device can be used for two or more production lines. However, testing in a separate X-ray NDT test device is time-consuming, as the circuit board has to be brought into the X-ray NDT test device from the production line, and the entire circuit board has to be re-examined there, this time with X-radiation instead of light.